EmptyNode

A placeholder node that renders nothing and takes no space.

Basic Usage

new EmptyNode()

Use Cases

Placeholder for Conditional Content

// Return EmptyNode when nothing should be shown
ViewModel.ErrorChanged
    .Select(error => string.IsNullOrEmpty(error)
        ? (ILayoutNode)new EmptyNode()
        : new TextNode(error).WithForeground(Color.Red))
    .AsLayout()

Spacer Between Elements

Layouts.Vertical()
    .WithChild(header.Height(1))
    .WithChild(new EmptyNode().Height(1))  // 1-row spacer
    .WithChild(content.Fill())

Flexible Spacer

// Push content to edges
Layouts.Horizontal()
    .WithChild(leftContent.WidthAuto())
    .WithChild(new EmptyNode().WidthFill())  // Takes remaining space
    .WithChild(rightContent.WidthAuto())

Default for ConditionalNode

// EmptyNode is the default else content
new ConditionalNode(
    condition,
    thenNode: visibleContent)  // else is EmptyNode

Important Notes

WARNING

Never use null as a layout node. Always use EmptyNode as a placeholder.

// Bad - null breaks the layout tree
condition ? content : null

// Good - EmptyNode is a valid placeholder
condition ? content : new EmptyNode()

API Reference

Constructor

public EmptyNode()

Behavior

• Measure() returns Size(0, 0) by default
• Render() does nothing
• Can be given size constraints to act as a spacer

Spacer Pattern

// Fixed spacer
new EmptyNode().Height(2)          // 2-row vertical spacer
new EmptyNode().Width(4)           // 4-column horizontal spacer

// Flexible spacer
new EmptyNode().Fill()             // Fill remaining height
new EmptyNode().WidthFill()        // Fill remaining width

Source Code

View EmptyNode implementation

// Copyright (c) Petabridge, LLC. All rights reserved.
// Licensed under the Apache 2.0 license. See LICENSE file in the project root for full license information.

using Termina.Rendering;

namespace Termina.Layout;

/// <summary>
/// An empty layout node that renders nothing and takes no space.
/// Useful as a placeholder or for conditional rendering.
/// </summary>
public sealed class EmptyNode : LayoutNode
{
    public EmptyNode()
    {
        WidthConstraint = new SizeConstraint.Fixed(0);
        HeightConstraint = new SizeConstraint.Fixed(0);
    }

    /// <inheritdoc />
    public override Size Measure(Size available) => Size.Zero;

    /// <inheritdoc />
    public override void Render(IRenderContext context, Rect bounds)
    {
        // Nothing to render
    }
}